\documentclass{article}
\usepackage[x11names, rgb]{xcolor}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{snakes,arrows,shapes}
\usepackage{amsmath}
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\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{0pt}%
\usetikzlibrary{automata}%

\begin{document}
\pagestyle{empty}
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\enlargethispage{100cm}
% Start of code
\begin{tikzpicture}[>=latex',join=bevel,]
\tikzstyle{every state}=[draw=blue!50,very thick,fill=blue!20]%
\node (q0) at (34bp,106bp) [state] {$\{q_{6}\}$};
  \node (q6) at (106bp,106bp) [state] {$\{q_{4}\}$};
  \node (q2) at (106bp,282bp) [state] {$\{q_{0}\}$};
  \node (q4) at (106bp,194bp) [state] {$\{q_{5}\}$};
  \node (q3) at (178bp,194bp) [state] {$\{q_{1}\}$};
  \node (q7) at (178bp,106bp) [state] {$\{q_{2}\}$};
  \node (q1) at (106bp,18bp) [state] {$\{q_{3}\}$};
  \node (q5) at (34bp,194bp) [state] {$\{q_{7}\}$};
  \draw [->] (q0) ..controls (58bp,77bp) and (74bp,57bp)  .. node[auto] {$\overline{b}$} (q1);
  \draw [->] (q6) ..controls (106bp,76bp) and (106bp,60bp)  .. node[auto] {$\overline{c}$} (q1);
  \draw [->] (q2) ..controls (82bp,253bp) and (66bp,233bp)  .. node[auto] {$a$} (q5);
  \draw [->] (q2) ..controls (106bp,252bp) and (106bp,236bp)  .. node[auto] {$\overline{c}$} (q4);
  \draw [->] (q2) ..controls (130bp,253bp) and (146bp,233bp)  .. node[auto] {$\overline{b}$} (q3);
  \draw [->] (q4) ..controls (87bp,167bp) and (77bp,153bp)  .. (68bp,142bp) .. controls (64bp,138bp) and (60bp,133bp)  .. node[auto] {$a$} (q0);
  \draw [->] (q4) ..controls (112bp,165bp) and (116bp,152bp)  .. (124bp,142bp) .. controls (130bp,134bp) and (139bp,127bp)  .. node[auto] {$\overline{b}$} (q7);
  \draw [->] (q3) ..controls (159bp,167bp) and (149bp,153bp)  .. (140bp,142bp) .. controls (136bp,138bp) and (132bp,133bp)  .. node[auto] {$a$} (q6);
  \draw [->] (q3) ..controls (178bp,164bp) and (178bp,148bp)  .. node[auto] {$\overline{c}$} (q7);
  \draw [->] (q7) ..controls (154bp,77bp) and (138bp,57bp)  .. node[auto] {$a$} (q1);
  \draw [->] (q5) ..controls (21bp,167bp) and (17bp,154bp)  .. (19bp,142bp) .. controls (20bp,139bp) and (21bp,136bp)  .. node[auto] {$\overline{c}$} (q0);
  \draw [->] (q5) ..controls (40bp,165bp) and (44bp,152bp)  .. (52bp,142bp) .. controls (58bp,134bp) and (67bp,127bp)  .. node[auto] {$\overline{b}$} (q6);
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\end{tikzpicture}
% End of code

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\end{document}
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